| /* |
| * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| * |
| */ |
| |
| package sun.jvm.hotspot.utilities; |
| |
| import java.io.*; |
| import java.util.*; |
| import sun.jvm.hotspot.debugger.*; |
| import sun.jvm.hotspot.gc.shared.*; |
| import sun.jvm.hotspot.memory.*; |
| import sun.jvm.hotspot.oops.*; |
| import sun.jvm.hotspot.runtime.*; |
| |
| /** Finds all paths from roots to the specified set of objects. NOTE: |
| currently only a subset of the roots known to the VM is exposed to |
| the SA: objects on the stack, static fields in classes, and JNI |
| handles. These should be most of the user-level roots keeping |
| objects alive. */ |
| |
| public class LivenessAnalysis { |
| // Used for debugging this code |
| private static final boolean DEBUG = false; |
| |
| private LivenessAnalysis() {} |
| |
| public static LivenessPathList computeAllLivenessPaths(Oop target) { |
| LivenessPathList list = computeAllLivenessPaths(target, true); |
| if ((list == null) || (list.size() == 0)) { |
| // Dead object |
| return null; |
| } |
| return list; |
| } |
| |
| //--------------------------------------------------------------------------- |
| // Internals only below this point |
| // |
| |
| // Returns true if a new path was completed, otherwise false |
| // indicating there were no more paths to complete. |
| // |
| // The trimPathsThroughPopularObjects flag alters the behavior of |
| // the returned results. If true, then if multiple paths to |
| // different roots all go through a particular popular object, those |
| // paths will be truncated and only one (arbitrary one) will be be |
| // returned. On the other hand, if the target object itself is |
| // popular and there are multiple distinct paths to it (indicating |
| // that there are multiple objects pointing directly to it) then all |
| // of those paths will be reported. |
| private static LivenessPathList computeAllLivenessPaths(Oop target, boolean trimPathsThroughPopularObjects) { |
| ReversePtrs rev = VM.getVM().getRevPtrs(); |
| if (rev == null) { |
| throw new RuntimeException("LivenessAnalysis requires ReversePtrs to have been computed"); |
| } |
| |
| // Currently the reverse pointer analysis returns non-null results |
| // only for live objects |
| if (rev.get(target) == null) { |
| // Object is dead |
| return null; |
| } |
| |
| // HashSet of Oops acting as a bit mask indicating which ones have |
| // already been traversed |
| Set/*<Oop>*/ visitedOops = new HashSet/*<Oop>*/(); |
| |
| // IdentityHashMap of LivenessElements acting as a bit mask |
| // indicating which roots have already been traversed |
| Map/*<LivenessElement, LivenessElement>*/ visitedRoots = |
| new IdentityHashMap/*<LivenessElement, LivenessElement>*/(); |
| |
| visitedOops.add(target); |
| |
| // Construct the initial LivenessPath |
| LivenessPathList list = new LivenessPathList(); |
| { |
| LivenessPath path = new LivenessPath(); |
| path.push(new LivenessPathElement(target, null)); |
| list.add(path); |
| } |
| |
| // Iterate until done |
| while (true) { |
| // See if there are any incomplete paths left |
| LivenessPath path = null; |
| |
| for (int i = list.size() - 1; i >= 0; i--) { |
| LivenessPath tmp = list.get(i); |
| if (!tmp.isComplete()) { |
| path = tmp; |
| break; |
| } |
| } |
| |
| // If no incomplete paths left, return |
| if (path == null) { |
| return list; |
| } |
| |
| // Try to complete this path |
| |
| // Remove the path from the list of reported ones in |
| // anticipation of completing it |
| list.remove(path); |
| |
| try { |
| // Fetch next set of reverse pointers for the last object on |
| // the list |
| ArrayList/*<LivenessPathElement>*/ nextPtrs = |
| rev.get(path.peek().getObj()); |
| |
| // Depending on exactly what the reverse pointers analysis |
| // yields, these results may be null, although currently they |
| // won't be |
| if (nextPtrs != null) { |
| // Iterate these |
| for (Iterator iter = nextPtrs.iterator(); iter.hasNext(); ) { |
| LivenessPathElement nextElement = (LivenessPathElement) iter.next(); |
| // See whether we've visited this element yet |
| if ((nextElement.isRoot() && (visitedRoots.get(nextElement) == null)) || |
| (!nextElement.isRoot() && !visitedOops.contains(nextElement.getObj()))) { |
| // Show we've visited this one |
| if (nextElement.isRoot()) { |
| visitedRoots.put(nextElement, nextElement); |
| } else { |
| visitedOops.add(nextElement.getObj()); |
| } |
| |
| // Create a new LivenessPath for each one |
| LivenessPath nextPath = path.copy(); |
| nextPath.push(nextElement); |
| |
| // Regardless of whether we found a root, put the |
| // original path back on the list because we're going to |
| // do depth-first searching rather than breadth-first |
| list.add(path); |
| list.add(nextPath); |
| |
| // See whether this path is complete (i.e., it |
| // terminates in a root) |
| if (trimPathsThroughPopularObjects && nextElement.isRoot()) { |
| // Go back through the path list and remove all |
| // incomplete paths ending in any of the intermediate |
| // (non-root and non-terminal) nodes in this path. |
| // This has the effect of removing multiple paths |
| // going through popular objects. |
| for (int i = 1; i < nextPath.size() - 1; i++) { |
| LivenessPathElement el = nextPath.get(i); |
| int j = 0; |
| while (j < list.size()) { |
| LivenessPath curPath = list.get(j); |
| // We can use an object identity since these |
| // intermediate nodes are canonicalized via the |
| // ReversePtrsAnalysis |
| if (curPath.peek() == el) { |
| list.remove(curPath); |
| } else { |
| j++; |
| } |
| } |
| } |
| } |
| |
| // Do depth-first searching, not breadth-first |
| break; |
| } |
| } |
| } |
| } catch (Exception e) { |
| System.err.println("LivenessAnalysis: WARNING: " + e + |
| " during traversal"); |
| } |
| } |
| } |
| } |